The present invention relates to a fuel injection system for an externally ignited internal combustion engine.
The system operates on fuel which is continuously injected into the suction tube of the engine in which an air sensing element and an arbitrarily operable throttle valve are disposed in series. The air sensing element is displaced by and in proportion to the throughgoing quantity of air against a restoring force. In the course of its excursion the air sensing element displaces a movable component of a valve which is disposed in the fuel supply line and which is intended for metering a quantity of fuel in proportion to the quantity of air. The above-noted restoring force is supplied by liquid under pressure which is delivered continuously under constant, but arbitrarily variable pressure through a control pressure conduit and which exerts a force on a control plunger transferring the restoring force and projecting with its one front face into a pressure chamber. The pressure of the pressurized liquid is variable by at least one pressure control valve which is controllable as a function of the engine parameters and which contains a temperature-dependent control element.
Fuel injection systems of this type are designed to automatically provide a good fuel-air mixture for all operating conditions of the internal combustion engine so as to burn the fuel as completely as possible and thus prevent toxic gases from being produced, or at least considerably reduce the toxic gases while obtaining maximum performance of the internal combustion engine, with minimum fuel consumption. The quantity of fuel must therefore be very accurately metered in accordance with the requirements of each operating state of the internal combustion engine.
In the case of known fuel injection systems of this type, the quantity of fuel which is metered is, as far as possible, proportionate to the quantity of air flowing through the suction tube of the engine. The ratio of the quantity of fuel which is metered to the quantity of air may be varied by changing the restoring force on the air sensing element as a function of the operating parameters by means of a pressure control valve.
It has been found that during the warm-up phase of the internal combustion engine the fuel-air mixture can be substantially leaner during stationary operation of the engine than when the throttle valve is suddenly opened. Accordingly, both the fuel consumption and the emission of toxic substances can be lowered during the warm-up phase of the engine by providing a lean fuel-air mixture during stationary operation of the engine and a temporarily enriched mixture when the throttle valve is suddenly opened.